1. Field of the Invention
The present invention relates to a microscope apparatus which is employed for observation and/or examination of a specimen with the use of illumination light of plural different wavelength regions.
2. Description of the Related Art
Conventionally, optical microscopes are widely used in semiconductor manufacturing processes for defect inspection and structural observation of device patterns. In recent years, the device patterns have become increasingly miniaturized and complex at a rapid pace. Accordingly, there is a high demand for further improvement in resolution of the optical microscopes. To achieve this goal, ultraviolet microscopes have been developed as described in Japanese Patent Applications Laid-Open No. 2006-154237, No. 2003-322801, and No. 2002-90640. These ultraviolet microscopes realize high resolution by using ultraviolet radiation as illumination light. The ultraviolet microscope uses ultraviolet radiation of a wide wavelength region ranging from a near-ultraviolet (NUV) region (i.e., radiation with the wavelength from 300 to 400 nm) to a deep-ultraviolet (DUV) region (i.e., radiation with the wavelength from 200 to 300 nm) as the illumination light.
Materials used in the semiconductor devices, such as Al and Cu, exhibit different reflectance and absorptance depending on the wavelength region of the ultraviolet radiation. The ultraviolet microscope realizes the defect inspection, structural observation, and the like utilizing this characteristic. For example, the wavelength region of the ultraviolet radiation used for the illumination is changed during the observation of a semiconductor device. Corresponding change in the reflectance of a device material is reflected in the change in pixel values of an observation image, and thus detected. Based on the detected change in reflectance, the device material is identified.
However, in the conventional ultraviolet microscopes, the change in reflectance of a specimen corresponding to the change in the wavelength region of ultraviolet radiation is not accurately reflected in the change in pixel values of the observation image, due to spectral output characteristic (i.e., distribution characteristic of emission spectrum) of a light source, spectral transmittance characteristic of an optical system of the microscope as a whole, spectral sensitivity characteristic of an imager that generates the observation image, and the like. For example, even when the changed wavelength region of ultraviolet radiation as the illumination actually causes the 1.5 times increase in reflectance of the specimen, the change in pixel values of the observation image sometimes does not show an accurate 1.5 times increase.
Further, when the wavelength region of the ultraviolet radiation used as the illumination is widened, another problem may arise in addition to the inaccurate correspondence between the change in reflectance of the specimen and the change in pixel values of the observation image. Namely, increased energy of ultraviolet radiation irradiated onto the specimen can damage the specimen significantly. Specifically, when a semiconductor device on which a resist is applied is used as a specimen, excessive ultraviolet radiation may break the resist. In addition, when the ultraviolet radiation of a wider wavelength region is employed, the imager receives increased amount of observation light, which may cause saturation of the observation image, in other words, which may cause brightness saturation of the imager.